02202cam a22002537 4500001000600000003000500006005001700011008004100028100002200069245009100091260006600182490005100248500002000299520097400319530006101293538007201354538003601426690009901462690018601561710004201747830008601789856003701875856003601912t0185NBER20180217235225.0180217s1995 mau||||fs|||| 000 0 eng d1 aHeckman, James J.10aInstrumental Variablesh[electronic resource]:bA Cautionary Tale /cJames J. Heckman. aCambridge, Mass.bNational Bureau of Economic Researchc1995.1 aNBER technical working paper seriesvno. t0185 aSeptember 1995.3 aThis paper considers the use of instrumental variables to estimate the mean effect of treatment on the treated. It reviews previous work on this topic by Heckman and Robb (1985, 1986) and demonstrates that (a) unless the effect of treatment is the same for everyone (conditional on observables), or (b) treatment effects are variable across persons but the person-specific component of the variability not forecastable by observables does not determine participation in the program, widely-used instrumental variable methods produce inconsistent estimators of the parameter of interest. Neither assumption is very palatable. The first assumes a homogeneity that is implausible. The second assumes either very rich data available to the econometrician or that the persons being studied either do not have better information than the econometrician or that they do not use it. Instrumental variable methods do not provide a general solution to the evaluation problem. aHardcopy version available to institutional subscribers. aSystem requirements: Adobe [Acrobat] Reader required for PDF files. aMode of access: World Wide Web. 7aC14 - Semiparametric and Nonparametric Methods: General2Journal of Economic Literature class. 7aC31 - Cross-Sectional Models • Spatial Models • Treatment Effect Models • Quantile Regressions • Social Interaction Models2Journal of Economic Literature class.2 aNational Bureau of Economic Research. 0aTechnical Working Paper Series (National Bureau of Economic Research)vno. t0185.4 uhttp://www.nber.org/papers/t018541uhttp://dx.doi.org/10.3386/t0185